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Phil, Mechanical Engineer

Category: HVAC

Satisfied Customers: 6596

Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial

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I have a Lennox HP26-036-7P heat pump.
In cooling mode

Customer Question

I have a Lennox HP26-036-7P heat pump.

In cooling mode the unit intermittently runs correctly but then at times runs for 30-60 minutes normally but then is unable to cool.

After the 30-60 minutes, the duct temperature slowly rises (over another 30 minutes) from 56-57 degrees up to the ambient temperature of the house.

The outside temperature when I tested was 82 degrees. The indoor temperature was 76. The thermostat was set to 70.

I checked the filters to ensure there are no restrictions. According to the service tech (who has been here twice) the gas pressures are on specification. Unfortunately (?) the machine has worked correctly while the tech was here so he was not able to diagnose the problem.

I've read that the reversing value can sometimes stick and prevent proper cooling. I've tried the suggested gentle tapping with a small mallet to determine if this is the issue. It has no effect on the unit.

This is a link to the manual if you need it for referencehttp://completeheating.ca/manuals/LennoxHP26.pdf

You are definitely on the right track with inspecting the reversing valve and the equipment itself.

You can however be distracted by getting involved with the room temperature... that lags the actual problem you are attempting to detect.

If you focus very directly on the unit itself, as it operates in cooling mode and with the suction line from the inside coil running cool or not, you will be able to spot the exact instant that the machine fails to cool.... and at that instant you will notice where the problem lies.

The suction line is the fattest copper tube attached to the outside unit if it is split system. the suction line as it attaches to the outside unit is insulated ..you will have to cut a slot in the insulation at times to feel the tube.

(I couldn't the link you provided to work just now. I will try to get it to open later. In the meantime tell me if your unit is package that sits outside, or if the part that blows the cold air is inside the house or not.)

For instance if the suction line suddenly starts warming up and you notice that the compressor just went off 10 seconds earlier, then you know it is a controls problem not a reversing valve problem.

If on the other hand you notice the compressor stays running but the suction line coming from the inside cooling coil warms up slightly... then it is likely a problem with the reversing valve.

Spend some time looking the situation over from that perspective... sitting next to the outside unit. Let me know what you can determine. We can go from there.

My unit is a split unit. The inside unit is a Lennox CB29M-46-1P. I have been concentrating on the outside unit assuming that if the issue is cooling related that it must be the place to look. I hope that is a good assumption...

I can access the cooling line with the rear panel off of the unit. I can confirm that the line begins to warm at some point even though the thermostat display says 'Cooling On'.

I didn't mention before, but after the Cooling cycle is completed (from cool duct temp back to ambient), I have to shut the system off for an hour or so before the system will begin cooling again. Not sure if this is relevant....

I will babysit the outside unit as suggested to get a better sense of when it fails.

- You should not have to remove the back panel of the outside unit to access the suction line, With the back panel removed you can allow the condenser fan to suck air though that opening rather that the condenser coil... that will lead to the compressor over heating.

- You can put your hand on the *compressor (big black, roundish, weighs 100 pounds or so) to see if its running... if it is running the *smallest tube attached will run hot enough to *burn you. Thats how you tell if he compressor is running or not.without using instruments.your remark that the unit has to sit for an hour before it can be reset by cycling the thermostat, is important information. It means the compressor is going off on one of it safety cut outs.

The primary suspect is a dirty condenser coil on the outside unit.. the big finned thing like a car radiator... clean it by ***blasting*** water from the garden hose pressed tight to the fins in order to blow water ***between*** each square inch of finned surface... do that until water blows out the other side of the coil.

DO THIS WITH THE POWER TURNED OFF TO THE UNIT AT ITS DISCONNECT SWITCH ON THE OUTSIDE WALL... and don't get any water on the electricals or fan motor... wrap them in plastic and be careful... its not an easy job.

If the unit is over 5 years old and has not been cleaned that way, this will very likely cure the problem. Let the unit dry out for an hour before you turn it back on.

That is the first step in any case...IF the unit is more than a few years old.

____________

If that fails there are many other less likely causes we can check as long as you continue to rate my remarks *positively and not negatively we keep going without any time limit. I hold the question open in that case.

The HP26 has the compressor hidden behind a protective cover that provides shielding (against weather from the inside) and prevents the sucking of air that you describe. A picture is attached showing the guts of the unit. The only way to see the compressor is by removing the back panel (See picture below)

Dirty coils...hmmm. Although there are no leaves or other large dirt bits visible, the last two years the technician recommended and applied an anti-corrosion spray to the coils. The coils are weathered (grey-white oxidation on them) possibly due to my location - a few miles from the ocean and the unit is constantly hit by salty air. Perhaps 12 years in this salty environment has taken it's toll on the coils...

The condenser coil needs to be chemically cleaned of its salt corrosion and dirt accumulations.... after 12 years in such an environment and showing aluminum oxide on the fins... a dirty condenser coil, or one with the aluminum fins separating from the copper tubes is the prime suspect here.

Your service man was correct in applying the anti corrosion treatment... the coils need to be cleaned chemically down to the bare metal before that is applied, and that can be risky for corrosion damaged coils.

He sounds like he might be competent to me, if thats the case he should make all these assessments on site based on what he can see.

_________

The other thing to know is that a 12 year old unit in any condition is not worth any investment over $300 or so... the fan is long since over due to fail, same with the compressor.

Tell me if the fan on the outside unit stops when the compressor stops running and the suction line goes warm or not. If the fan keeps running and the compressor stops, the compressor is going off on its internal overload in most cases. If both the fan and compressor stop the unit could be going off on its high pressure safety cut off switch.

let me know about those issues.Tell me when the unit was last worked on... there is a chance in that case that the system was over charged by a few ounces of refrigerant in that case.

And... tell me what your monthly electricity bill is in the summer as compared to the winter... from that I can assess the viability of changing out the cooling part of the system to a much more efficient system than was commonly available in 2011

There will be a SEER rating stamped on the name plate of that unit... see if you can find it and tell me what it says. If the SEER rating is 12 or less, you can probably reduce your cooling costs by 40 to 50% per year. making the current unit even less viable to repair.

a new unit can also be bought with coils not subject to salt air corrosion, or coated at the factory.

First however we need your service man to assess exactly what is going on with the coil, how much amperage the unit is drawing, and what the head pressures and suction pressures are along with the corresponding indoor and outdoor temperatures.

If you tell him that he will be first in line when it comes to replacing the system he might do that assessment for you at no charge...it will take him an hour or less, and needs to be done during the heat of the day around 2 pm... not earlier.

The other thing to know is that a 12 year old unit in any condition is not worth any investment over $300 or so... the fan is long since over due to fail, same with the compressor.

Wow! I thought they were good for 25 years! I don’t think the salesman mentioned that 12 years ago! Can newer outdoor units be matched with the existing indoor unit? Or would both units have to be replaced?

Tell me if the fan on the outside unit stops when the compressor stops running and the suction line goes warm or not. If the fan keeps running and the compressor stops, the compressor is going off on its internal overload in most cases. If both the fan and compressor stop the unit could be going off on its high pressure safety cut off switch.

The fan continues to run after the compressor stops (and the suction line begins to warm).

let me know about those issues. Tell me when the unit was last worked on... there is a chance in that case that the system was over charged by a few ounces of refrigerant in that case.

The unit was last worked on August of 2012. At that time the tech said the gas was perfect and did not need to be charged. He measured suction pressure at 56 psi and head at 225 psi (). The anti-corrosion spray was applied as suggested earlier.

This problem has been intermittent since May of 2011. In 2011 a tech visited as well. Anti-corrosion spray was applied but I can’t find the service sheet to tell me the other details.

And... tell me what your monthly electricity bill is in the summer as compared to the winter... from that I can assess the viability of changing out the cooling part of the system to a much more efficient system than was commonly available in 2011

In 2001... Regardless, I’m not too worried about the cost of cooling. Our hot season is short (about 2 months) so the total cost of cooling is not that significant. My electricity bill for the year is $3200.

There will be a SEER rating stamped on the name plate of that unit... see if you can find it and tell me what it says. If the SEER rating is 12 or less, you can probably reduce your cooling costs by 40 to 50% per year. making the current unit even less viable to repair.

The SEER is 14.05. HSPF is 8.4 and is more important in my climate - I see newer units are up to about 25% more efficient.

a new unit can also be bought with coils not subject to salt air corrosion, or coated at the factory.That would be nice!

First however we need your service man to assess exactly what is going on with the coil, how much amperage the unit is drawing, and what the head pressures and suction pressures are along with the corresponding indoor and outdoor temperatures.

If you tell him that he will be first in line when it comes to replacing the system he might do that assessment for you at no charge...it will take him an hour or less, and needs to be done during the heat of the day around 2 pm... not earlier.

I have him booked for Thursday Aug 1 at 2:00PM. Unfortunately, I can't get him any sooner!

Hello again I have seen heat pumps last 20+ years...its not common however. And will not generally warrant more than minor repairs.

The newer ones have deceptive warranties, the long lasting compressors are guaranteed for 10 years....but you can spend a thousand dollars or more keeping it running until then. Average life span is about 15 years... many are worn out at 10 years. Depends on the quality of the installation and other factors.

Tell me if the fan on the outside unit stops when the compressor stops running and the suction line goes warm or not. If the fan keeps running and the compressor stops, the compressor is going off on its internal overload in most cases. If both the fan and compressor stop the unit could be going off on its high pressure safety cut off switch.

The fan continues to run after the compressor stops (and the suction line begins to warm).

*** The compressor is over heating, most likely due to dirty or fins clogged with salt water corrosion deep between the fins.... less likely because of other reasons.

let me know about those issues. Tell me when the unit was last worked on... there is a chance in that case that the system was over charged by a few ounces of refrigerant in that case.

The unit was last worked on August of 2012. At that time the tech said the gas was perfect and did not need to be charged. He measured suction pressure at 56 psi and head at 225 psi (). The anti-corrosion spray was applied as suggested earlier.

**** You have an honest and capable repair man on your hands...don't loose his card. feed him a sandwich next time he comes by. Those pressure readings are close to ideal especially if the condensing unit is more than 50 feet away from the indoor unit. (ideal is 60 psig if unit and the cooling coil are within 15 feet) His gages could have been off by 2 psig as well.

The suction pressure would also be low because the cooling coil inside is partially clogged up, no doubt about that after 12 years, the blower vanes also pack with dirt in that time span... those should be cleaned as well. your service people will charge you about $250 for that.

This problem has been intermittent since May of 2011. In 2011 a tech visited as well. Anti-corrosion spray was applied but I can’t find the service sheet to tell me the other details.

And... tell me what your monthly electricity bill is in the summer as compared to the winter... from that I can assess the viability of changing out the cooling part of the system to a much more efficient system than was commonly available in 2011

In 2001... Regardless, I’m not too worried about the cost of cooling. Our hot season is short (about 2 months) so the total cost of cooling is not that significant. My electricity bill for the year is $3200.

****Thats not out of line for a medium to larger size home.

There will be a SEER rating stamped on the name plate of that unit... see if you can find it and tell me what it says. If the SEER rating is 12 or less, you can probably reduce your cooling costs by 40 to 50% per year. making the current unit even less viable to repair.

The SEER is 14.05. HSPF is 8.4 and is more important in my climate - I see newer units are up to about 25% more efficient.

*** Thats pretty good efficiency...a new unit would take a bit too long to pay off on energy savings alone.... lets hope its just a clogged condenser coil.

a new unit can also be bought with coils not subject to salt air corrosion, or coated at the factory.That would be nice!

** there are two options along those lines, copper tube and copper or cu pro-nickel fins (drives the cost up by a few thousand dollars and may not pay off in your only semi corrosive environment).... and 'epoxy coated coils) which add a few hundred dollars and will be a good investment in your case.)

*****Before you spend money on replacement though have the coil completed cleaned with inhibited acids down to bare metal...and checked out as I mentioned in my earlier post... watch the work being done yourself so you know what to look for.

My indoor unit is about 30 ft from the outside unit. Should the pressure be higher if the outdoor unit is closer to the inside unit?

On the date/time (Aug 13.2012 3:30 PM) the pressures I gave earlier were taken the outside temperature was 70 degrees. The humidex bumped the temp to about 77. The indoor temp would have been around 72-73.

The house is about 1650 sq feet on two floors for a total of 3300. I guess that's average?

There is a thermostatic control below the muffler on the discharge line of the compressor. This thermostat was originally used to turn a service light on/off on the inside thermostat. The only reason i mention this device is that it is baked - like it was subject to higher temperatures than it should have been.

Here is the info about the device...

My current thermostat doesn't have the service light so I don't know if the device is working properly. Regardless, I thought it was interesting that the device is 'baked'. I suspect this also supports your theory that the compressor is overloading (so much so that a nearby component is being cremated).

Inhibited acid...that could be nasty where ground water contamination is a concern. I understand the need for the cleaning but wouldn't want somebody using a squeeze bottle of it in my backyard. I'll have to ask the tech about options in this respect.

I've washed the coils as suggested but it did not do much. I'm sure the suggested acid cleaning is the only way.

I really appreciate your help with this - I've learned a lot. Can I do a Rate to Finish but still keep the dialog open so that after the tech visit next Thursday I can relay the results to you?

My indoor unit is about 30 ft from the outside unit. Should the pressure be higher if the outdoor unit is closer to the inside unit?

***** Yes, depending on the diameter of the suction line and how many fittings in it... generally the actual coil pressure is about 2 psig higher than the pressure taken at the outside unit.

--------------

On the date/time (Aug 13.2012 3:30 PM) the pressures I gave earlier were taken the outside temperature was 70 degrees. The humidex bumped the temp to about 77. The indoor temp would have been around 72-73.

* The condenser coil at the outside unit rated at 14 seer runs about 20 degrees hotter than the outside air...so that if the outside air is 70F, the unit is condensing at 90F (if the condenser fan is constant speed and running, let me know if thats true or not)CLICK HERE FOR PRESSURE TEMPERATURE CHART THAT INCLUDES R-22 notice the head pressure should be 168 psig to 181 psig. Your unit was running at a lot higher head pressure. That would be because of a dirty condenser or a condenser fan slowed down a 'head pressure control system' that slows the condenser fan when running in cooling mode in cooler weather.. I will send this note now, then review the wiring diagram you sent for that feature.

--------------

The house is about 1650 sq feet on two floors for a total of 3300. I guess that's average?

* average is about 1500 square feet, you have a large house by any standards.. your electric bill is in a range or a bit low for that sort of house.

_____________

There is a thermostatic control below the muffler on the discharge line of the compressor. This thermostat was originally used to turn a service light on/off on the inside thermostat. The only reason i mention this device is that it is baked - like it was subject to higher temperatures than it should have been.

*that thermostat is for use in heating mode only, warning if the head pressure gets too low according to note you posted a photo copy of.

It might be wired to turn the compressor off if the head pressure gets too high as well... I need to check the diagram for that feature.

My current thermostat doesn't have the service light so I don't know if the device is working properly. Regardless, I thought it was interesting that the device is 'baked'. I suspect this also supports your theory that the compressor is overloading (so much so that a nearby component is being cremated).

* its probably not relevant.. cleaning the condenser first is a priority...have your tech supply the data Ive asked for and assess the condenser coil for corrosion.

--------------

Inhibited acid...that could be nasty where ground water contamination is a concern. I understand the need for the cleaning but wouldn't want somebody using a squeeze bottle of it in my backyard. I'll have to ask the tech about options in this respect.

* the slight amount of acid that isn't neutralized in cleaning the coil will be neutralized by a few cubic feet of the ground.. its generally mild enough that it doesn't harm the lawn. By contrast acid rain from coal burning power plants, even just one is a few billion times worse 24/7... its a trace contamination at the worst.

________________

I've washed the coils as suggested but it did not do much. I'm sure the suggested acid cleaning is the only way.

*If you got the water to blast through the coil so it came out the other side, you got it 95% clean enough.

------------

I really appreciate your help with this - I've learned a lot. Can I do a Rate to Finish but still keep the dialog open so that after the tech visit next Thursday I can relay the results to you?

*you can do a 'rate and finish' but it will not end our conversation since I will hold the dialog box open for you, with no time limit

* thanks, if the fan were not running the pessure would have 500+ psig.

so that the pressure you were runninat at, indicates a 30% clogged condenser which would definitely cause the problem you are having.

OR.... an over charge of refigerant, However if the system works in heating mode, it would not be an overcharge issue.

* average is about 1500 square feet, you have a large house by any standards.. your electric bill is in a range or a bit low for that sort of house.

I'm in a maritime climate - winters are relatively warm and summers relatively cool. That's why the costs are probably lower than you were expecting.

* its probably not relevant.. cleaning the condenser first is a priority...have your tech supply the data Ive asked for and assess the condenser coil for corrosion.

I will.

d.

Okay.

*If you got the water to blast through the coil so it came out the other side, you got it 95% clean enough.

The water came through. I spayed from the outside in and from the inside out (turned off the breaker and removed the top cover to get access)

That should have been good enough to solve the current problem.... unless the fins have begun corroding away from the copper tubes...in that case a new condenser will cost about $1200 installed... the money is better spent towards a new unit, and new evaporator coil running on R410a... SEER 14 is ok in your climate. The corrosion on the coil and fin tube separateion and corrosion clogging, needs to be verified however.

The compressor needs to be checked for its 'full load amperage' draw..(F:LA) if it is running below the FLA and still going off on its over load, which overload can be verified by your technician... we need to know if it is the compressors internal overload, or some other over load. there is a 95% chance it is the compressors internal overload. Requires a new compressor, not at all a good choice given the condenser corrosion issue.

...have your tech supply the data Ive asked for

-----------

Please list the measurements that are needed. That will help me with my communication to the tech.

* I need the following in the heat of the day. Not the morning.

- head and suction pressures and the indoor and outdoor dry bulb temperatures unadjusted at the time. Humidity is not a factor in those applications.

- Compressor amp draw at the time.

- Compressor FLA rating stamped on its name plate.. (not the LRA rating which is 3 times higher,)

- Pump down test on the compressor to 10 psig only (not lower) cycle the compressor a few times with the liquid line valve closed... tell me how long it takes the suction pressure to rise to 80 psig with the compressor shut off.. I need that number in seconds.

- Temperature of the air coming off of the condenser coil at the same time.

Its possible to replace the outside unit without changing the coil inside, but not at all advisable... R410a runs at much higher pressures than R-22 did, and exceeds the test pressure limits of the older R-22 components. A new inside coil wholesales for under $500.

I need the LRA rating so I can compare the actual amperage draw against it.... as soon as those tests i mentioned are done I can do that for you.

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